The overall objectives of this project are to study the mechanism of electron transfer in flavoenzymes where the coenzyme functions as a redox-active catalyst and the catalytic mechanism of oxynitrilase, an atypical flavoenzyme which catalyzes a non-redox reaction. Studies with oxynitrilase will focus on the role of the coenzyme as a structural component of the active site. The mechanism of hydrogen transfer and the role of flavin-oxygen adducts in catalysis will be investigated in studies with flavoprotein oxidases and hydroxylases, respectively. Studies with different classes of flavoproteins will be conducted to evaluate the hypothesis that the reaction of enzyme-bound 5-deazaflavin with peroxides may be useful as an active site probe. The proposed research will involve spectroscopic, kinetic, and structural analysis of reactions involving use of substrate analogues and modified flavin derivatives.